1. Field of the Invention
The present invention relates generally to a seal element for sealing along a rotary member. More particularly, the present invention relates to a coiled split sealing element having a sealing lip and the method of manufacture of such seal. The coiled split lip sealing element finds particular use in process and transfer pumps having a stuffing box.
2. Background of the Related Art
Seal elements are widely used to seal pump and machine shafts. In many machines employed in manufacturing, it is necessary to provide a seal between a rotary member, such as a shaft, and a stationary member, such as a housing. Likewise, seals are employed between rotary housings and stationary shafts, pipes, studs, etc. Although conventionally structured from wear resistant materials, seals nevertheless in time will wear away or become corroded. Therefore, seals are replaced at relatively frequent intervals.
Integral seal elements are seals that are integrally formed, that is not split. Integral seals are widely employed. However, they generally require the removal of machine parts which surround or are adjacent to the part being sealed, such as the rotary member, in order to allow ample access room to permit seal replacement. Disassembly and re-assembly of such parts often requires a great expenditure of time and labor, with a consequent monetary cost. For example, where a shaft extends from a housing, the exterior bearing or journal member for such shaft, as well as the coupling parts to the shaft and external parts of the housing, may have to be removed before the integral seals can be brought into access position for removal. The cost for such repair may be considerable, as product is lost during the interval of machine down-time.
One type of prior art integral seal is manufactured with a compression lip. So-called "lip seals" have a flexible hinged lip on the seal base that permits for firmer pressure against the radial face of the shaft or other item to which the seal element is attached. The lip permits a somewhat self-adjusting seal, in particular when the shaft is dynamic. Lip seals are frequently molded of elastomeric material, such as nitrile rubber, or polymeric material, such as polytetrafluoroethylene. The are not infrequently used to surround a shaft in a sealing relationship to provide a fluid or gas tight chamber in a housing from which the shaft extends.
Integral seals may also be deflected in such manner as to form so-called "sleeve seals". Sleeve seals are generally flat or conical radially extending washers which are deflectable both axially and radially by a relatively rotating surface to form a seal.
Split seal elements are used in many applications wherein integral solid seals would be difficult or time-consuming to install. Employment of split seals may reduce the time for replacing a seal from 24 hours (if a solid integral seal was employed) to less than an hour. Split seal elements are frequently bolted together, squeezed together with an "O" ring or squeezed together on a taper. Bolted split seal elements are relatively expensive, and generally require a large amount of space for the seal. Split seal elements that are squeezed together with an "O" ring are generally limited to use with respect to shafts having a low rotational speed, since centrifugal forces tend to open the split halves at high rotational speeds. While split seal elements which are squeezed together with a taper are somewhat more adaptable, the alignment of surfaces has to be near perfect in order to prevent leakage. Further, while generally providing for more flexibility in the shaft diameter ranges in which they may be employed, split seal elements like integral-solid seals suffer from a relatively inflexibility in the array of rotary diameters on which they may be employed.
Spiral packing seals have also been employed in the art (see, e.g., U.S. Pat. No. 3,945,649). Such seals are generally split. Such seals are usually employed to seal a shaft in a fluid tight manner to prevent leakage. The shaft is sealed by winding the spiral member around the shaft in a stuffing box. Such seals are not infrequently used when the vessel contains a fluid of high pressure, for instance, in centrifugal and plunger pumps.
Both integral seals and split seals have been employed in so-called "mechanical seal" systems. A typical mechanical seal would include a stationary sealing ring sealed by an o-ring gasket to the housing and a spring loaded sealing member secured to the shaft or sleeve on the shaft that rotates with the shaft. The rotating sealing member is usually spring loaded in some fashion to insure that, as the sealing surfaces wear, the spring will keep the rotating sealing member engaged with the stationary sealing ring. Mechanical seals are frequently used to seal stuffing boxes of process and transfer pumps.
Seals may be made of numerous materials, such as, for example, rubber, cast iron, plastics, polytetrafluoroethylene ("PTFE"), and other such materials that perform the sealing function. The material from which a seal is fabricated is generally dictated by the application in which it is intended to be used. For example, while PTFE seals have good corrosion resistance, they have proven unsatisfactory under high external loads at high temperatures and pressures due to high creep relaxation and cold flow problems. Further such seals are prone to failure due to an inadequate modulus of elasticity resulting in the seal not be elastically urged firmly against the inside diameter of the shaft to which it is attached.
All conventional seals suffer from drawbacks, primarily related to a improper sealing (and therefore leakage), and to the need for frequent replacement of such seals when they are attached to moving shafts. Therefore, there is a need for an improved shaft sealing element which would provide an improved seal around the shaft, require less frequent replacement and that would provide for easy exchange of the used seal for a new seal in requiring minimal dissassembly of the machine parts surrounding the shaft when the seals are exchanged.